Build fails on Linux ARM64

[martin-g]

Trying to build graphmap2 on openEuler 20.03 LTS ARM64 fails with:

mkdir -p obj_linux/codebase/seqlib/src/libs/libdivsufsort-2.0.1-64bit/
g++ -static-libgcc -static-libstdc++ -D__cplusplus=201103L -I"./src/" -I"/usr/include/" -I"codebase/seqlib/src/libs/seqan-library-2.0.1/include" -I"codebase/seqlib/src/libs/libdivsufsort-2.0.1-64bit/" -Icodebase/argumentparser/src -Icodebase/seqlib/src -Icodebase/gindex/src -DRELEASE_VERSION -g -O3 -fdata-sections -ffunction-sections -c -fmessage-length=0 -ffreestanding -fopenmp -m64 -std=c++11 -Werror=return-type -pthread  -o obj_linux/codebase/seqlib/src/libs/libdivsufsort-2.0.1-64bit/utils.o codebase/seqlib/src/libs/libdivsufsort-2.0.1-64bit/utils.cpp
g++: error: unrecognized command line option ‘-m64’
make: *** [Makefile:128: obj_linux/codebase/seqlib/src/libs/libdivsufsort-2.0.1-64bit/utils.o] Error 1

According to https://stackoverflow.com/a/58244182/497381 -m64 is x86_64 specific flag.
I will try to provide a PR with support for both CPU architectures!

$ g++ --version
g++ (GCC) 7.3.0
$ uname -a
Linux mgrigorov-arm64 4.19.90-2205.3.0.0149.oe1.aarch64 #1 SMP Wed May 11 12:53:17 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux

[julien-faye]

+1 for support for ARM64 !

[martin-g]

Will be fixed with #23